Reduction in sulfate inhibition of microbial dechlorination of polychlorinated biphenyls in Hudson and Grasse River sediments through fatty acid supplementation.

Microbial dechlorination of polychlorinated biphenyls (PCBs) in aquatic sediments may reduce the need for dredging for remediation. To better understand this biotransformation route under different geochemical conditions, the influence of sulfate on dechlorination in sediments from the Hudson River and the Grasse River spiked with two PCB mixtures (PCB 5/12, 64/71, 105/114 and 149/153/170 in Mixture 1 and PCB 5/12, 64/71, 82/97/99, 144/170 in Mixture 2) was investigated. The results showed that PCB dechlorination was partially inhibited in the sulfate-amended sediment microcosms. The rate, extent and preference of dechlorination were mainly controlled by the indigenous differences (sulfate, carbon content etc.) in sediment, but also affected by the PCB mixture composition. An increase of Dehalococcoides 16S rRNA genes coincided with the resumption of dechlorination. Dechlorination preferences were identified using a modified dechlorination pathway analysis approach. The low carbon content and high background sulfate Hudson sediment exhibited more para dechlorination targeting flanked para chlorines. The high carbon content and low background sulfate Grasse sediment preferentially removed more para-flanked meta chlorines than flanked para chlorines. The supplementation of fatty acids (acetate or a mixture of acetate, propionate and butyrate) dramatically increased PCB dechlorination in the Grasse sediment by resuming ortho-flanked meta dechlorination. Rare ortho removals were found in the Grasse sediment after adding fatty acids. This study suggests that supplementary fatty acids might be used to stimulate PCB dechlorination under sulfate reducing conditions, but the effectiveness largely depends on sediment geochemistry.

Influence of application of manganese ore in constructed wetlands on the mechanisms and improvement of nitrogen and phosphorus removal.

Vertical up-flow constructed wetlands (CWs) with manganese ore (Mn ore) as media (M-CWs) were developed to treat simulated polluted river water. The results showed that the average removal efficiencies for NH4-N, NO3-N, TN and TP were 91.74%, 83.29%, 87.47% and 65.12% in M-CWs, respectively, which were only 79.12%, 72.90%, 75.85% and 43.23% in the CWs without Mn ore (C-CWs). Nutrient mass balance showed that nitrogen (N) removal was improved by enhanced microbial processes, media storage and plant uptake in M-CWs. Moreover, almost 50% of phosphorus (P) was retained by media storage because of the adsorption processes on Mn ore. It was found that addition of Mn ore enhanced denitrification as the relative abundance of denitrifying bacteria increased. The produced Mn(II) and more abundant Gammaproteobacteria confirmed alternative N removal pathways including anoxic nitrification coupled to Mn ore reduction and denitrification using Mn(II) as electron donor. Mn(II) concentration in the effluent of M-CWs was below the drinking water limit of 0.1 mg/L, which makes them environmentally-friendly.

Bench-scale evaluation of aerosol delivery for biostimulation and bioaugmentation in the vadose zone.

Aerosol delivery was evaluated for distributing biostimulation and bioaugmentation amendments in vadose zones. This technique involves transporting amendments as micron-scale aerosol droplets in injected gas. Microcosm experiments were designed to characterize reductive dechlorination of trichloroethene (TCE) under unsaturated conditions when delivering components as aerosols. Delivering amendments and/or microbes as aqueous aerosols resulted in complete dechlorination of TCE, similar to controls operated under saturated conditions. Reductive dechlorination was achieved with manual injection of a bioaugmentation culture suspended in soybean oil into microcosms. However, aerosol delivery of the culture in soybean oil induced little reductive dechlorination activity. Overall, the results indicate that delivery as aqueous aerosols may be a viable option for delivery of amendments to enhance vadose zone bioremediation at the field-scale.

Organic cofactors in the metabolism of Dehalococcoides mccartyi strains.

Dehalococcoides mccartyi strains are strictly anaerobic organisms specialized to grow with halogenated compounds as electron acceptor via a respiratory process. Their genomes are among the smallest known for free-living organisms, and the embedded gene set reflects their strong specialization. Here, we briefly review main characteristics of published Dehalococcoides genomes and show how genome information together with cultivation and biochemical experiments have contributed to our understanding of Dehalococcoides physiology and biochemistry. We extend this approach by the detailed analysis of cofactor metabolism in Dehalococcoides strain CBDB1. Dehalococcoides genomes were screened for encoded proteins annotated to contain or interact with organic cofactors, and the expression of these proteins was analysed by shotgun proteomics to shed light on cofactor requirements. In parallel, cultivation experiments testing for vitamin requirements showed that cyanocobalamin (vitamin B12), thiamine and biotin were essential supplements and that cyanocobalamin could be substituted by dicyanocobinamide and dimethylbenzimidazole. Dehalococcoides genome analysis, detection of single enzymes by shotgun proteomics and inhibition studies confirmed the expression of the biosynthetic pathways for pyridoxal-5-phosphate, flavin nucleotides, folate, S-adenosylmethionine, pantothenate and nicotinic acids in strain CBDB1. Haem/cytochromes, quinones and lipoic acids were not necessary for cultivation or dechlorination activity and no biosynthetic pathways were identified in the genomes.

A remediation performance model for enhanced metabolic reductive dechlorination of chloroethenes in fractured clay till.

A numerical model of metabolic reductive dechlorination is used to describe the performance of enhanced bioremediation in fractured clay till. The model is developed to simulate field observations of a full scale bioremediation scheme in a fractured clay till and thereby to assess remediation efficiency and timeframe. A relatively simple approach is used to link the fermentation of the electron donor soybean oil to the sequential dechlorination of trichloroethene (TCE) while considering redox conditions and the heterogeneous clay till system (clay till matrix, fractures and sand stringers). The model is tested on lab batch experiments and applied to describe sediment core samples from a TCE-contaminated site. Model simulations compare favorably to field observations and demonstrate that dechlorination may be limited to narrow bioactive zones in the clay matrix around fractures and sand stringers. Field scale simulations show that the injected donor is expected to be depleted after 5 years, and that without donor re-injection contaminant rebound will occur in the high permeability zones and the mass removal will stall at 18%. Long remediation timeframes, if dechlorination is limited to narrow bioactive zones, and the need for additional donor injections to maintain dechlorination activity may limit the efficiency of ERD in low-permeability media. Future work should address the dynamics of the bioactive zones, which is essential to understand for predictions of long term mass removal.

Feasibility of sunflower oil cake degradation with three different anaerobic consortia.

Sunflower oil cake (SuOC) is the solid by-product from the sunflower oil extraction process and an important pollutant waste because of its high organic content. For the anaerobic digestion of SuOC three different industrial reactors were compared as inoculum sources. This was done using a biochemical methane production (BMP) test. Inoculum I was a granular biomass from an industrial reactor treating soft-drink wastewaters. Inoculum II was a flocculent biomass from a full-scale reactor treating biosolids generated in an urban wastewater treatment plant. Inoculum III was a granular biomass from an industrial reactor treating brewery wastes. The highest kinetic constant for methane production was achieved using inoculum II. The inoculum sources were analyzed through PCR amplification of 16S rRNA genes and fingerprinting before (t = 0) and after the BMP test (t = 12 days). No significant differences were found in the bacterial community fingerprints between the beginning and the end of the experiments. The bacterial and archaeal communities of inoculum II were further analyzed. The main bacteria found in this inoculum belong to Alphaproteobacteria and Chloroflexi. Of the Archaea detected, Methanomicrobiales and Methanosarcinales made up practically the whole archaeal community. The results showed the importance of selecting an appropriate inoculum in short term processes due to the fact that the major microbial constituents in the initial consortia remained stable throughout anaerobic digestion.

Selective utilization of exogenous amino acids by Dehalococcoides ethenogenes strain 195 and its effects on growth and dechlorination activity.

Bacteria of the genus Dehalococcoides are important members of bioremediation communities because of their ability to detoxify chloroethenes to the benign end product ethene. Genome-enabled studies conducted with Dehalococcoides ethenogenes 195 have revealed that two ATP-binding cassette (ABC)-type amino acid transporters are expressed during its exponential growth stages. In light of previous findings that Casamino Acids enhanced its dechlorination activity, we hypothesized that strain 195 is capable of importing amino acids from its environment to facilitate dechlorination and growth. To test this hypothesis, we applied isotopomer-based dilution analysis with (13)C-labeled acetate to differentiate the amino acids that were taken up by strain 195 from those synthesized de novo and to determine the physiological changes caused by the significantly incorporated amino acids. Our results showed that glutamate/glutamine and aspartate/asparagine were almost exclusively synthesized by strain 195, even when provided in excess in the medium. In contrast, phenylalanine, isoleucine, leucine, and methionine were identified as the four most highly incorporated amino acids, at levels >30% of respective proteinogenic amino acids. When either phenylalanine or all four highly incorporated amino acids were added to the defined mineral medium, the growth rates, dechlorination activities, and yields of strain 195 were enhanced to levels similar to those observed with supplementation with 20 amino acids. However, genes for the putative ABC-type amino acids transporters and phenylalanine biosynthesis exhibited insignificant regulation in response to the imported amino acids. This study also demonstrates that using isotopomer-based metabolite analysis can be an efficient strategy for optimizing nutritional conditions for slow-growing microorganisms.

Bioaugmentation for treatment of dense non-aqueous phase liquid in fractured sandstone blocks.

Laboratory experiments were performed in discretely fractured sandstone blocks to evaluate the use of bioaugmentation to treat residual dense non-aqueous phase liquid (DNAPL) tetrachloroethene (PCE). Significant dechlorination of PCE and growth of Dehalococcoides spp. (DHC) occurred within the fractures. DNAPL dissolution was enhanced during bioaugmentation by up to a factor of approximately 3.5, with dissolved PCE concentrations at or near aqueous solubility. The extent of dechlorination and DNAPL dissolution enhancement were dependent upon the fracture characteristics, residence time in the fractures, and dissolved concentration of PCE. No relationship was observed between planktonic DHC concentrations exiting the fracture and the observed extents of PCE dechlorination and DNAPL dissolution. Measured planktonic DHC concentrations exiting the fracture increased with increasing flow rate and bioaugmentation dosage, suggesting that these parameters may be important for distribution of DHC to treat dissolved chlorinated ethenes migrating downgradient of the DNAPL source. Bioaugmentation dosage, for the DHC dosages and conditions studied, did not have a measurable impact on DNAPL dissolution or dechlorination within the fractures themselves. Overall, these results indicate that bioaugmentation may be a viable remedial option for treating DNAPL sources in bedrock.